Calculator KB-39
RMS, Peak, and Peak-to-Peak Voltage Calculator
Why is the mains voltage 230 V, but the capacitor after the bridge rectifier charges to 325 V?
Result
In brief: Convert RMS to peak voltage and peak-to-peak voltage for sine, rectified, square, and triangular waveforms: RMS, average, and peak values, and form factor. Example: RMS value: 230 V.
Calculation example
| Waveform | Sine |
|---|---|
| Known values | RMS |
| Value | 230 V |
| RMS value | 230 V |
|---|---|
| Peak | 325.27 V |
| Peak-to-peak | 650.54 V |
| Average rectified value | 207.07 V |
| Crest factor | 1.414 |
| Form factor | 1.111 |
How it is calculated
Uavg = 2 · Upk / π
The RMS value heats a resistor just like the same DC voltage. Peak voltage matters when calculating insulation and capacitors; RMS matters for power. Basic multimeters give accurate readings only for a pure sine wave. Other waveforms require a True RMS meter.
What to look for
- The peak voltage of 230 V mains is about 325 V. Capacitors after the bridge rectifier should be rated for at least 400 V.
- An oscilloscope shows peak-to-peak and peak voltage, while a multimeter usually shows RMS. This is a common source of confusion when taking measurements.
Frequently asked questions
What is the peak amplitude of 230 V mains voltage?
230 · √2 ≈ 325 V, with a peak-to-peak swing of about 650 V. Insulation and capacitors are rated for these values.
How do I convert Vpp to Vrms?
For a sine wave, Vrms = Vpp / (2√2) ≈ 0.354 · Vpp: 10 Vpp gives 3.54 V RMS. For a square wave, Vrms = Vpp / 2; for a triangle wave, Vpp / (2√3).
Why do you need a True RMS multimeter?
A basic meter measures the average value and scales it for a sine wave. With PWM, after a dimmer, or with an inverter's modified sine wave, it gives inaccurate readings, while a True RMS meter measures the RMS value.
